A wide area network (WAN) is a network which covers more than one single geographical area, and uses communications circuits and systems to connect a plurality of network nodes. “Wide area” coverage is defined by a number of base repeater stations which are typically distributed geographically over an area, perhaps in a partially overlapping manner, and are connected over a wired or wireless network. Often these stations are distributed in such a way that no one station could cover the same geographic area by itself (however this isn't always the reason for such a wide area network). This enables a first mobile wireless subscriber station within coverage of a first fixed base repeater station to communicate with other (second, third, etc.) subscriber stations within coverage of remote (second, third, etc.) base repeater stations, and enables a first mobile wireless subscriber station to travel across a greater geographic area and still obtain services provided by the plurality of interconnected base repeater stations.
In other examples, a local area network (LAN) may be used to interconnect a plurality of locally-arranged base repeater stations configured so as to provide fully or partially overlapping coverage areas within a contiguous geographic region.
Wireless WANs/LANs may utilize communication technologies such as WIMAX (Worldwide Interoperability for Microwave Access), UMTS (Universal Mobile Telecommunications Service), GPRS (General Packet Radio Service), CDMA (Code Division Multiple Access), GSM (Global System for Mobile communications), CDPD (Cellular Digital Packet Data), HSDPA (High-Speed Downlink Packet Access), 3G (third generation), 4G (fourth generation), and the like, to transfer data. Wired WANs/LANs may utilize Data Over Cable Service Interface Specifications (DOCSIS), Digital subscriber line (DSL), Canopy, Ethernet, T1, or the like to transfer data.
Within a WAN or LAN (e.g., a network), a variety of communication scenarios can co-exist. For example, one use of the network is to enable a group call (i.e. one subscriber station transmitting to many subscriber stations who are listening, perhaps some of which may be distributed across the network of radio sites).
A common WAN over which group calls can be sent is the Public Internet. The Internet is a worldwide, publicly accessible series of interconnected computer networks that transmit data by packet switching using the standard Internet Protocol (IP). It is a “network of networks” that consists of millions of smaller domestic, academic, business, and government networks, which together carry various information and services.
One typical way of providing group communications amongst subscriber stations is to implement a trunked radio communications system. In a trunked radio communications system, subscriber stations use a pool of channels that are assigned on an as-needed basis for new talkgroup calls. Thus, all talkgroups are served by all channels. The trunked radio system takes advantage of the probability that not all talkgroups need a channel for communication at the same time. Estimates are made about how much load a typical user presents to the system in terms of calls per hour and duration of each call. For a traffic load, fewer channels are required since all talkgroups are served by all channels. Combining this with the number of users on the system, and the acceptable quality of service (QoS), determines how many trunked channels are required to satisfactorily serve the number of users. With a given number of channels, a much greater number of talkgroups can be accommodated as compared with conventional radio systems. Hence, a primary purpose of a trunked radio system is the efficient utilization of channels allowing for more users to carry many conversations over a fewer number of distinct channels.
A trunked radio system can be either a centralized trunked radio system or a decentralized trunked radio system. A centralized trunked radio system uses a dedicated or exclusive controller that assigns traffic channels upon request. Other terms that sometimes refer to the central controller include trunking controller, site controller, resource allocator, channel allocator, controller, and other like terms. The subscriber stations constantly monitor a control channel for channel assignment instructions from the central controller. In order to start a group call, a subscriber station requests that a channel be allocated for its use, and the central controller transmits instructions telling the subscriber stations in the group to switch to a traffic channel assigned for that call.
A decentralized trunked radio system, however, does not require the use of an exclusive controller. The intelligence or control function for assignment of a channel to a call is distributed amongst base repeater stations and/or subscriber stations in the wireless communications network. For example, in one case one of the base repeater stations out of the plurality of base repeater stations may be designated a rest channel repeater, and all subscriber stations will idle on the channel (e.g., the rest channel) assigned to the rest channel repeater (the rest channel) and monitor the rest channel for new calls. Requests to start a new call will be received by the rest channel repeater and assigned a traffic channel. All subscriber stations wishing to participate in the new call will then move to the new traffic channel for the call, and once completed, return to the rest channel. The particular repeater designated as a rest channel repeater may change from time to time, perhaps due to detected interference and/or start-up rest channel arbitration procedures between repeaters at a radio site.
In another case, a new call request received at a rest channel repeater will be assigned to the current rest channel as the traffic channel for the new call. In this case, instead of those subscriber stations not participating in the new call remaining on the rest channel, those subscriber stations not participating in the new call move to a new rest channel while those subscriber stations wishing to participate in the new call remain on the old rest channel (which has now become a traffic channel for the new call). The new rest channel may be assigned and/or detected in a number of different ways.
Because the rest channel at a decentralized trunked radio system may change over time, it becomes difficult for a subscriber station roaming between geographic areas covered by varying base repeater stations to discover what channel any one particular base repeater station is currently using as a rest channel (e.g., the only channel that is continuously or periodically keyed-on by the repeater) and thus becomes difficult for the subscriber station to sample signal strengths of neighboring coverage areas. Because the subscriber station must search for a current rest channel at each potential neighboring site, the amount of time it takes for the subscriber station to determine if it would be advantageous to hand-off service increases, and the chance that the subscriber station misses a call announcement in its current geographic coverage area increases (as it scans for rest channels in neighboring areas for measurements). Accordingly, there is a need for a method and system for more efficiently scanning and roaming between radio sites in a network of interconnected radio sites having dynamic rest-channel base repeater stations.
Skilled artisans will appreciate that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of embodiments of the present invention.
The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.